In conventional sputtering of quartz the usual sputter deposition chamber utilizes a cathode and an anode spaced in opposed relationship with the wafers resting upon the anode. The spacing between the cathode and anode is normally fixed depending upon the size of the plates and other deposition parameters of the system. Since wafers worked upon in batch quantities normally have the same thickness, then the distance between the top surface of a given wafer on the anode plate to the cathode is essentially constant.
Despite this uniformity of distance it has been found that the field effects and deposition field intensity within the sputtering region vary from wafer to wafer. Accordingly, the conventional sputtering systems result in nonuniformity of quartz deposition upon the wafer. For example, in a conventional 40 MH.sub.z sputtering system adapted to deposit about 25,000 Angstroms of quartz upon each wafer, it would not be unusual to have a variation of as much as 3,000 Angstroms in the thickness of quartz deposited upon a given wafer, particularly if the wafer is located at the outer periphery of the anode plate where field effect variations are more significant. This uniformity variation is generally unsatisfactory for the processing of wafers to achieve high yields.
In particular, such a thickness variation in the quartz leads to difficulty in opening of vias in later processing steps, which results in failure of product.
In prior work described in IBM Technical Disclosure Bulletin, Vol. 19, No. 2, July 1976 pages 516-517 one of the inventors herein discloses that, in part, the variations in quartz deposition thickness can be correlated to the spacing of the top surface of the wafer from the adjacent surface of the source material. Consequently compensation for such differences in distribution can be provided by varying the individual spacing of the wafers and source in accordance with coating differences found.
One solution proposed in that publication, to achieve uniformity, utilized spacers under wafers on the anode plate to change the dimensional spacing of a given wafer with respect to the cathode.
The aforementioned system modified quartz distribution deposition thickness to some extent, particularly with respect to variations occurring in one wafer versus another in a batch. However, the solution proposed does not solve thickness variation problems existing on a given wafer within a batch.
Consequently, a need still exists for a method and apparatus for attaining satisfactory quartz deposition uniformity throughout the surface of single layers within a batch processing sputtering system.